1. Field of the Invention
This invention relates generally to an RF treatment apparatus, and more particularly to an RF treatment apparatus operable in bipolar or monopolar modes to deliver directable thermal energy to a target tissue site.
2. Description of Related Art
Treatment of cellular tissues usually requires direct contact of target tissue with a medical instrument, usually by surgical procedures exposing both the target and intervening tissue to substantial trauma. Often, precise placement of a treatment probe is difficult because of the location of a target tissue in the body or the proximity of the target tissue to easily damaged, critical body organs, nerves, or other components.
High frequency currents are used in electrocautery procedures for cutting human tissue especially when a bloodless incision is desired or when the operating site is not accessible with a normal scalpel but presents an access for a thin instrument through natural body openings such as the esophagus, intestines or urethra. Examples include the removal of prostatic adenomas, bladder tumors or intestinal polyps. In such cases, the high-frequency current is fed by a surgical probe into the tissue to be cut. The resulting dissipated heat causes boiling and vaporization of the cell fluid at this point, whereupon the cell walls rupture and the tissue is separated. The frequency of the current for this use must be above ca. 300 kHz in order to avoid adverse nerve and/or muscle responses.
Destruction of cellular tissues in situ has been used in the treatment of many diseases and medical conditions alone or as an adjunct to surgical removal procedures. It is often less traumatic than surgical procedures and may be the only alternative where other procedures are unsafe. Ablative treatment devices have the advantage of using a destructive energy which is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of circulating fluids and other natural body processes.
Microwave, radio frequency, acoustical (ultrasound) and light energy (laser) devices, and tissue destructive substances have been used to destroy malignant, benign and other types of cells and tissues from a wide variety of anatomic sites and organs. Tissues treated include isolated carcinoma masses and, more specifically, organs such as the prostate, glandular and stromal nodules characteristic of benign prostate hyperplasia. These devices typically include a catheter or cannula which is used to carry a radio frequency electrode or microwave antenna through a duct to the zone of treatment and apply energy diffusely through the duct wall into the surrounding tissue in all directions.
Current open procedures for treatment of target tissues are extremely disruptive and cause a great deal of damage to healthy tissue. Accordingly, there has recently been a fair amount of emphasis of minimally invasive procedures for target tissue destruction and removal.
Among the problems associated with all of these procedures is the requirement that highly localized heat be produced at depths of several centimeters beneath the surface of the body. Certain techniques have been developed with microwave radiation and ultrasound to focus energy at various desired depths. RF applications may be used at depth during surgery. However, the extent of localization is generally poor with the result that healthy tissue may be harmed. Induction heating gives rise to poor localization of the incident energy as well. Although induction heating may be achieved by placing an antenna on the surface of the body, superficial eddy currents are generated in the immediate vicinity of the antenna when it is driven using RF current, and unwanted surface heating occurs with little coupled to the underlying tissue. Thus, noninvasive procedures for providing heat to internal target tissue sites have had difficulties is substantial specific and selective treatment.
Hyperthermia, which can be from an RF or microwave source, applied heat to tissue but does not exceed 45 degrees C. so that normal cells survive. In thermotherapy, heat energy of greater than 45 degrees C. is applied, resulting in histological damage and the denaturization of proteins. Hyperthermia has been applied more recently for cell necrosis of a target tissue site. In hyperthermia, it is desirable to induce a state of hyperthermia that is localized by interstitial current heating to a specific area while concurrently insuring minimum thermal damage to healthy surrounding tissue. Often, the target tissue site is located subcutaneously and addressing the target tissue site requires either surgery, endoscopic procedures or exits healing requires either surgery, endoscopic procedures or external radiation. It is difficult to externally induce hyperthermia in deep body tissue because current density is diluted due to its absorption by healthy tissue. Additionally, a portion of the RF energy is reflected at the muscle/fat and bone interfaces which adds to the problem of depositing a known quantity of energy directly on a small target tissue site.
There is a need for an RF treatment apparatus to minimally invasively create cell necrosis in a target tissue site. There is a further need for an RF treatment apparatus that provides directional delivery of RF energy to a target tissue site. Another need exists for an RF ablation apparatus which can be operated in bipolar or monopolar modes to deliver directable thermal energy to a targeted tissue site.